1 // SPDX-License-Identifier: GPL-2.0-only
5 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
6 * Copyright (C) 2008-2009 Red Hat, Inc.
7 * Copyright (C) 2015 Red Hat, Inc.
9 * Some part derived from fs/eventfd.c (anon inode setup) and
10 * mm/ksm.c (mm hashing).
13 #include <linux/list.h>
14 #include <linux/hashtable.h>
15 #include <linux/sched/signal.h>
16 #include <linux/sched/mm.h>
18 #include <linux/poll.h>
19 #include <linux/slab.h>
20 #include <linux/seq_file.h>
21 #include <linux/file.h>
22 #include <linux/bug.h>
23 #include <linux/anon_inodes.h>
24 #include <linux/syscalls.h>
25 #include <linux/userfaultfd_k.h>
26 #include <linux/mempolicy.h>
27 #include <linux/ioctl.h>
28 #include <linux/security.h>
29 #include <linux/hugetlb.h>
31 int sysctl_unprivileged_userfaultfd __read_mostly
= 1;
33 static struct kmem_cache
*userfaultfd_ctx_cachep __read_mostly
;
35 enum userfaultfd_state
{
41 * Start with fault_pending_wqh and fault_wqh so they're more likely
42 * to be in the same cacheline.
46 * fault_pending_wqh.lock
50 * To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
51 * since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
52 * also taken in IRQ context.
54 struct userfaultfd_ctx
{
55 /* waitqueue head for the pending (i.e. not read) userfaults */
56 wait_queue_head_t fault_pending_wqh
;
57 /* waitqueue head for the userfaults */
58 wait_queue_head_t fault_wqh
;
59 /* waitqueue head for the pseudo fd to wakeup poll/read */
60 wait_queue_head_t fd_wqh
;
61 /* waitqueue head for events */
62 wait_queue_head_t event_wqh
;
63 /* a refile sequence protected by fault_pending_wqh lock */
64 struct seqcount refile_seq
;
65 /* pseudo fd refcounting */
67 /* userfaultfd syscall flags */
69 /* features requested from the userspace */
70 unsigned int features
;
72 enum userfaultfd_state state
;
75 /* memory mappings are changing because of non-cooperative event */
77 /* mm with one ore more vmas attached to this userfaultfd_ctx */
81 struct userfaultfd_fork_ctx
{
82 struct userfaultfd_ctx
*orig
;
83 struct userfaultfd_ctx
*new;
84 struct list_head list
;
87 struct userfaultfd_unmap_ctx
{
88 struct userfaultfd_ctx
*ctx
;
91 struct list_head list
;
94 struct userfaultfd_wait_queue
{
96 wait_queue_entry_t wq
;
97 struct userfaultfd_ctx
*ctx
;
101 struct userfaultfd_wake_range
{
106 static int userfaultfd_wake_function(wait_queue_entry_t
*wq
, unsigned mode
,
107 int wake_flags
, void *key
)
109 struct userfaultfd_wake_range
*range
= key
;
111 struct userfaultfd_wait_queue
*uwq
;
112 unsigned long start
, len
;
114 uwq
= container_of(wq
, struct userfaultfd_wait_queue
, wq
);
116 /* len == 0 means wake all */
117 start
= range
->start
;
119 if (len
&& (start
> uwq
->msg
.arg
.pagefault
.address
||
120 start
+ len
<= uwq
->msg
.arg
.pagefault
.address
))
122 WRITE_ONCE(uwq
->waken
, true);
124 * The Program-Order guarantees provided by the scheduler
125 * ensure uwq->waken is visible before the task is woken.
127 ret
= wake_up_state(wq
->private, mode
);
130 * Wake only once, autoremove behavior.
132 * After the effect of list_del_init is visible to the other
133 * CPUs, the waitqueue may disappear from under us, see the
134 * !list_empty_careful() in handle_userfault().
136 * try_to_wake_up() has an implicit smp_mb(), and the
137 * wq->private is read before calling the extern function
138 * "wake_up_state" (which in turns calls try_to_wake_up).
140 list_del_init(&wq
->entry
);
147 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
149 * @ctx: [in] Pointer to the userfaultfd context.
151 static void userfaultfd_ctx_get(struct userfaultfd_ctx
*ctx
)
153 refcount_inc(&ctx
->refcount
);
157 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
159 * @ctx: [in] Pointer to userfaultfd context.
161 * The userfaultfd context reference must have been previously acquired either
162 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
164 static void userfaultfd_ctx_put(struct userfaultfd_ctx
*ctx
)
166 if (refcount_dec_and_test(&ctx
->refcount
)) {
167 VM_BUG_ON(spin_is_locked(&ctx
->fault_pending_wqh
.lock
));
168 VM_BUG_ON(waitqueue_active(&ctx
->fault_pending_wqh
));
169 VM_BUG_ON(spin_is_locked(&ctx
->fault_wqh
.lock
));
170 VM_BUG_ON(waitqueue_active(&ctx
->fault_wqh
));
171 VM_BUG_ON(spin_is_locked(&ctx
->event_wqh
.lock
));
172 VM_BUG_ON(waitqueue_active(&ctx
->event_wqh
));
173 VM_BUG_ON(spin_is_locked(&ctx
->fd_wqh
.lock
));
174 VM_BUG_ON(waitqueue_active(&ctx
->fd_wqh
));
176 kmem_cache_free(userfaultfd_ctx_cachep
, ctx
);
180 static inline void msg_init(struct uffd_msg
*msg
)
182 BUILD_BUG_ON(sizeof(struct uffd_msg
) != 32);
184 * Must use memset to zero out the paddings or kernel data is
185 * leaked to userland.
187 memset(msg
, 0, sizeof(struct uffd_msg
));
190 static inline struct uffd_msg
userfault_msg(unsigned long address
,
192 unsigned long reason
,
193 unsigned int features
)
197 msg
.event
= UFFD_EVENT_PAGEFAULT
;
198 msg
.arg
.pagefault
.address
= address
;
199 if (flags
& FAULT_FLAG_WRITE
)
201 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
202 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
203 * was not set in a UFFD_EVENT_PAGEFAULT, it means it
204 * was a read fault, otherwise if set it means it's
207 msg
.arg
.pagefault
.flags
|= UFFD_PAGEFAULT_FLAG_WRITE
;
208 if (reason
& VM_UFFD_WP
)
210 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
211 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
212 * not set in a UFFD_EVENT_PAGEFAULT, it means it was
213 * a missing fault, otherwise if set it means it's a
214 * write protect fault.
216 msg
.arg
.pagefault
.flags
|= UFFD_PAGEFAULT_FLAG_WP
;
217 if (features
& UFFD_FEATURE_THREAD_ID
)
218 msg
.arg
.pagefault
.feat
.ptid
= task_pid_vnr(current
);
222 #ifdef CONFIG_HUGETLB_PAGE
224 * Same functionality as userfaultfd_must_wait below with modifications for
227 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx
*ctx
,
228 struct vm_area_struct
*vma
,
229 unsigned long address
,
231 unsigned long reason
)
233 struct mm_struct
*mm
= ctx
->mm
;
237 VM_BUG_ON(!rwsem_is_locked(&mm
->mmap_sem
));
239 ptep
= huge_pte_offset(mm
, address
, vma_mmu_pagesize(vma
));
245 pte
= huge_ptep_get(ptep
);
248 * Lockless access: we're in a wait_event so it's ok if it
251 if (huge_pte_none(pte
))
253 if (!huge_pte_write(pte
) && (reason
& VM_UFFD_WP
))
259 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx
*ctx
,
260 struct vm_area_struct
*vma
,
261 unsigned long address
,
263 unsigned long reason
)
265 return false; /* should never get here */
267 #endif /* CONFIG_HUGETLB_PAGE */
270 * Verify the pagetables are still not ok after having reigstered into
271 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
272 * userfault that has already been resolved, if userfaultfd_read and
273 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
276 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx
*ctx
,
277 unsigned long address
,
279 unsigned long reason
)
281 struct mm_struct
*mm
= ctx
->mm
;
289 VM_BUG_ON(!rwsem_is_locked(&mm
->mmap_sem
));
291 pgd
= pgd_offset(mm
, address
);
292 if (!pgd_present(*pgd
))
294 p4d
= p4d_offset(pgd
, address
);
295 if (!p4d_present(*p4d
))
297 pud
= pud_offset(p4d
, address
);
298 if (!pud_present(*pud
))
300 pmd
= pmd_offset(pud
, address
);
302 * READ_ONCE must function as a barrier with narrower scope
303 * and it must be equivalent to:
304 * _pmd = *pmd; barrier();
306 * This is to deal with the instability (as in
307 * pmd_trans_unstable) of the pmd.
309 _pmd
= READ_ONCE(*pmd
);
314 if (!pmd_present(_pmd
))
317 if (pmd_trans_huge(_pmd
))
321 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
322 * and use the standard pte_offset_map() instead of parsing _pmd.
324 pte
= pte_offset_map(pmd
, address
);
326 * Lockless access: we're in a wait_event so it's ok if it
337 /* Should pair with userfaultfd_signal_pending() */
338 static inline long userfaultfd_get_blocking_state(unsigned int flags
)
340 if (flags
& FAULT_FLAG_INTERRUPTIBLE
)
341 return TASK_INTERRUPTIBLE
;
343 if (flags
& FAULT_FLAG_KILLABLE
)
344 return TASK_KILLABLE
;
346 return TASK_UNINTERRUPTIBLE
;
349 /* Should pair with userfaultfd_get_blocking_state() */
350 static inline bool userfaultfd_signal_pending(unsigned int flags
)
352 if (flags
& FAULT_FLAG_INTERRUPTIBLE
)
353 return signal_pending(current
);
355 if (flags
& FAULT_FLAG_KILLABLE
)
356 return fatal_signal_pending(current
);
362 * The locking rules involved in returning VM_FAULT_RETRY depending on
363 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
364 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
365 * recommendation in __lock_page_or_retry is not an understatement.
367 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
368 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
371 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
372 * set, VM_FAULT_RETRY can still be returned if and only if there are
373 * fatal_signal_pending()s, and the mmap_sem must be released before
376 vm_fault_t
handle_userfault(struct vm_fault
*vmf
, unsigned long reason
)
378 struct mm_struct
*mm
= vmf
->vma
->vm_mm
;
379 struct userfaultfd_ctx
*ctx
;
380 struct userfaultfd_wait_queue uwq
;
381 vm_fault_t ret
= VM_FAULT_SIGBUS
;
386 * We don't do userfault handling for the final child pid update.
388 * We also don't do userfault handling during
389 * coredumping. hugetlbfs has the special
390 * follow_hugetlb_page() to skip missing pages in the
391 * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
392 * the no_page_table() helper in follow_page_mask(), but the
393 * shmem_vm_ops->fault method is invoked even during
394 * coredumping without mmap_sem and it ends up here.
396 if (current
->flags
& (PF_EXITING
|PF_DUMPCORE
))
400 * Coredumping runs without mmap_sem so we can only check that
401 * the mmap_sem is held, if PF_DUMPCORE was not set.
403 WARN_ON_ONCE(!rwsem_is_locked(&mm
->mmap_sem
));
405 ctx
= vmf
->vma
->vm_userfaultfd_ctx
.ctx
;
409 BUG_ON(ctx
->mm
!= mm
);
411 VM_BUG_ON(reason
& ~(VM_UFFD_MISSING
|VM_UFFD_WP
));
412 VM_BUG_ON(!(reason
& VM_UFFD_MISSING
) ^ !!(reason
& VM_UFFD_WP
));
414 if (ctx
->features
& UFFD_FEATURE_SIGBUS
)
418 * If it's already released don't get it. This avoids to loop
419 * in __get_user_pages if userfaultfd_release waits on the
420 * caller of handle_userfault to release the mmap_sem.
422 if (unlikely(READ_ONCE(ctx
->released
))) {
424 * Don't return VM_FAULT_SIGBUS in this case, so a non
425 * cooperative manager can close the uffd after the
426 * last UFFDIO_COPY, without risking to trigger an
427 * involuntary SIGBUS if the process was starting the
428 * userfaultfd while the userfaultfd was still armed
429 * (but after the last UFFDIO_COPY). If the uffd
430 * wasn't already closed when the userfault reached
431 * this point, that would normally be solved by
432 * userfaultfd_must_wait returning 'false'.
434 * If we were to return VM_FAULT_SIGBUS here, the non
435 * cooperative manager would be instead forced to
436 * always call UFFDIO_UNREGISTER before it can safely
439 ret
= VM_FAULT_NOPAGE
;
444 * Check that we can return VM_FAULT_RETRY.
446 * NOTE: it should become possible to return VM_FAULT_RETRY
447 * even if FAULT_FLAG_TRIED is set without leading to gup()
448 * -EBUSY failures, if the userfaultfd is to be extended for
449 * VM_UFFD_WP tracking and we intend to arm the userfault
450 * without first stopping userland access to the memory. For
451 * VM_UFFD_MISSING userfaults this is enough for now.
453 if (unlikely(!(vmf
->flags
& FAULT_FLAG_ALLOW_RETRY
))) {
455 * Validate the invariant that nowait must allow retry
456 * to be sure not to return SIGBUS erroneously on
457 * nowait invocations.
459 BUG_ON(vmf
->flags
& FAULT_FLAG_RETRY_NOWAIT
);
460 #ifdef CONFIG_DEBUG_VM
461 if (printk_ratelimit()) {
463 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
472 * Handle nowait, not much to do other than tell it to retry
475 ret
= VM_FAULT_RETRY
;
476 if (vmf
->flags
& FAULT_FLAG_RETRY_NOWAIT
)
479 /* take the reference before dropping the mmap_sem */
480 userfaultfd_ctx_get(ctx
);
482 init_waitqueue_func_entry(&uwq
.wq
, userfaultfd_wake_function
);
483 uwq
.wq
.private = current
;
484 uwq
.msg
= userfault_msg(vmf
->address
, vmf
->flags
, reason
,
489 blocking_state
= userfaultfd_get_blocking_state(vmf
->flags
);
491 spin_lock_irq(&ctx
->fault_pending_wqh
.lock
);
493 * After the __add_wait_queue the uwq is visible to userland
494 * through poll/read().
496 __add_wait_queue(&ctx
->fault_pending_wqh
, &uwq
.wq
);
498 * The smp_mb() after __set_current_state prevents the reads
499 * following the spin_unlock to happen before the list_add in
502 set_current_state(blocking_state
);
503 spin_unlock_irq(&ctx
->fault_pending_wqh
.lock
);
505 if (!is_vm_hugetlb_page(vmf
->vma
))
506 must_wait
= userfaultfd_must_wait(ctx
, vmf
->address
, vmf
->flags
,
509 must_wait
= userfaultfd_huge_must_wait(ctx
, vmf
->vma
,
512 up_read(&mm
->mmap_sem
);
514 if (likely(must_wait
&& !READ_ONCE(ctx
->released
) &&
515 !userfaultfd_signal_pending(vmf
->flags
))) {
516 wake_up_poll(&ctx
->fd_wqh
, EPOLLIN
);
518 ret
|= VM_FAULT_MAJOR
;
521 * False wakeups can orginate even from rwsem before
522 * up_read() however userfaults will wait either for a
523 * targeted wakeup on the specific uwq waitqueue from
524 * wake_userfault() or for signals or for uffd
527 while (!READ_ONCE(uwq
.waken
)) {
529 * This needs the full smp_store_mb()
530 * guarantee as the state write must be
531 * visible to other CPUs before reading
532 * uwq.waken from other CPUs.
534 set_current_state(blocking_state
);
535 if (READ_ONCE(uwq
.waken
) ||
536 READ_ONCE(ctx
->released
) ||
537 userfaultfd_signal_pending(vmf
->flags
))
543 __set_current_state(TASK_RUNNING
);
546 * Here we race with the list_del; list_add in
547 * userfaultfd_ctx_read(), however because we don't ever run
548 * list_del_init() to refile across the two lists, the prev
549 * and next pointers will never point to self. list_add also
550 * would never let any of the two pointers to point to
551 * self. So list_empty_careful won't risk to see both pointers
552 * pointing to self at any time during the list refile. The
553 * only case where list_del_init() is called is the full
554 * removal in the wake function and there we don't re-list_add
555 * and it's fine not to block on the spinlock. The uwq on this
556 * kernel stack can be released after the list_del_init.
558 if (!list_empty_careful(&uwq
.wq
.entry
)) {
559 spin_lock_irq(&ctx
->fault_pending_wqh
.lock
);
561 * No need of list_del_init(), the uwq on the stack
562 * will be freed shortly anyway.
564 list_del(&uwq
.wq
.entry
);
565 spin_unlock_irq(&ctx
->fault_pending_wqh
.lock
);
569 * ctx may go away after this if the userfault pseudo fd is
572 userfaultfd_ctx_put(ctx
);
578 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx
*ctx
,
579 struct userfaultfd_wait_queue
*ewq
)
581 struct userfaultfd_ctx
*release_new_ctx
;
583 if (WARN_ON_ONCE(current
->flags
& PF_EXITING
))
587 init_waitqueue_entry(&ewq
->wq
, current
);
588 release_new_ctx
= NULL
;
590 spin_lock_irq(&ctx
->event_wqh
.lock
);
592 * After the __add_wait_queue the uwq is visible to userland
593 * through poll/read().
595 __add_wait_queue(&ctx
->event_wqh
, &ewq
->wq
);
597 set_current_state(TASK_KILLABLE
);
598 if (ewq
->msg
.event
== 0)
600 if (READ_ONCE(ctx
->released
) ||
601 fatal_signal_pending(current
)) {
603 * &ewq->wq may be queued in fork_event, but
604 * __remove_wait_queue ignores the head
605 * parameter. It would be a problem if it
608 __remove_wait_queue(&ctx
->event_wqh
, &ewq
->wq
);
609 if (ewq
->msg
.event
== UFFD_EVENT_FORK
) {
610 struct userfaultfd_ctx
*new;
612 new = (struct userfaultfd_ctx
*)
614 ewq
->msg
.arg
.reserved
.reserved1
;
615 release_new_ctx
= new;
620 spin_unlock_irq(&ctx
->event_wqh
.lock
);
622 wake_up_poll(&ctx
->fd_wqh
, EPOLLIN
);
625 spin_lock_irq(&ctx
->event_wqh
.lock
);
627 __set_current_state(TASK_RUNNING
);
628 spin_unlock_irq(&ctx
->event_wqh
.lock
);
630 if (release_new_ctx
) {
631 struct vm_area_struct
*vma
;
632 struct mm_struct
*mm
= release_new_ctx
->mm
;
634 /* the various vma->vm_userfaultfd_ctx still points to it */
635 down_write(&mm
->mmap_sem
);
636 /* no task can run (and in turn coredump) yet */
637 VM_WARN_ON(!mmget_still_valid(mm
));
638 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
)
639 if (vma
->vm_userfaultfd_ctx
.ctx
== release_new_ctx
) {
640 vma
->vm_userfaultfd_ctx
= NULL_VM_UFFD_CTX
;
641 vma
->vm_flags
&= ~(VM_UFFD_WP
| VM_UFFD_MISSING
);
643 up_write(&mm
->mmap_sem
);
645 userfaultfd_ctx_put(release_new_ctx
);
649 * ctx may go away after this if the userfault pseudo fd is
653 WRITE_ONCE(ctx
->mmap_changing
, false);
654 userfaultfd_ctx_put(ctx
);
657 static void userfaultfd_event_complete(struct userfaultfd_ctx
*ctx
,
658 struct userfaultfd_wait_queue
*ewq
)
661 wake_up_locked(&ctx
->event_wqh
);
662 __remove_wait_queue(&ctx
->event_wqh
, &ewq
->wq
);
665 int dup_userfaultfd(struct vm_area_struct
*vma
, struct list_head
*fcs
)
667 struct userfaultfd_ctx
*ctx
= NULL
, *octx
;
668 struct userfaultfd_fork_ctx
*fctx
;
670 octx
= vma
->vm_userfaultfd_ctx
.ctx
;
671 if (!octx
|| !(octx
->features
& UFFD_FEATURE_EVENT_FORK
)) {
672 vma
->vm_userfaultfd_ctx
= NULL_VM_UFFD_CTX
;
673 vma
->vm_flags
&= ~(VM_UFFD_WP
| VM_UFFD_MISSING
);
677 list_for_each_entry(fctx
, fcs
, list
)
678 if (fctx
->orig
== octx
) {
684 fctx
= kmalloc(sizeof(*fctx
), GFP_KERNEL
);
688 ctx
= kmem_cache_alloc(userfaultfd_ctx_cachep
, GFP_KERNEL
);
694 refcount_set(&ctx
->refcount
, 1);
695 ctx
->flags
= octx
->flags
;
696 ctx
->state
= UFFD_STATE_RUNNING
;
697 ctx
->features
= octx
->features
;
698 ctx
->released
= false;
699 ctx
->mmap_changing
= false;
700 ctx
->mm
= vma
->vm_mm
;
703 userfaultfd_ctx_get(octx
);
704 WRITE_ONCE(octx
->mmap_changing
, true);
707 list_add_tail(&fctx
->list
, fcs
);
710 vma
->vm_userfaultfd_ctx
.ctx
= ctx
;
714 static void dup_fctx(struct userfaultfd_fork_ctx
*fctx
)
716 struct userfaultfd_ctx
*ctx
= fctx
->orig
;
717 struct userfaultfd_wait_queue ewq
;
721 ewq
.msg
.event
= UFFD_EVENT_FORK
;
722 ewq
.msg
.arg
.reserved
.reserved1
= (unsigned long)fctx
->new;
724 userfaultfd_event_wait_completion(ctx
, &ewq
);
727 void dup_userfaultfd_complete(struct list_head
*fcs
)
729 struct userfaultfd_fork_ctx
*fctx
, *n
;
731 list_for_each_entry_safe(fctx
, n
, fcs
, list
) {
733 list_del(&fctx
->list
);
738 void mremap_userfaultfd_prep(struct vm_area_struct
*vma
,
739 struct vm_userfaultfd_ctx
*vm_ctx
)
741 struct userfaultfd_ctx
*ctx
;
743 ctx
= vma
->vm_userfaultfd_ctx
.ctx
;
748 if (ctx
->features
& UFFD_FEATURE_EVENT_REMAP
) {
750 userfaultfd_ctx_get(ctx
);
751 WRITE_ONCE(ctx
->mmap_changing
, true);
753 /* Drop uffd context if remap feature not enabled */
754 vma
->vm_userfaultfd_ctx
= NULL_VM_UFFD_CTX
;
755 vma
->vm_flags
&= ~(VM_UFFD_WP
| VM_UFFD_MISSING
);
759 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx
*vm_ctx
,
760 unsigned long from
, unsigned long to
,
763 struct userfaultfd_ctx
*ctx
= vm_ctx
->ctx
;
764 struct userfaultfd_wait_queue ewq
;
769 if (to
& ~PAGE_MASK
) {
770 userfaultfd_ctx_put(ctx
);
776 ewq
.msg
.event
= UFFD_EVENT_REMAP
;
777 ewq
.msg
.arg
.remap
.from
= from
;
778 ewq
.msg
.arg
.remap
.to
= to
;
779 ewq
.msg
.arg
.remap
.len
= len
;
781 userfaultfd_event_wait_completion(ctx
, &ewq
);
784 bool userfaultfd_remove(struct vm_area_struct
*vma
,
785 unsigned long start
, unsigned long end
)
787 struct mm_struct
*mm
= vma
->vm_mm
;
788 struct userfaultfd_ctx
*ctx
;
789 struct userfaultfd_wait_queue ewq
;
791 ctx
= vma
->vm_userfaultfd_ctx
.ctx
;
792 if (!ctx
|| !(ctx
->features
& UFFD_FEATURE_EVENT_REMOVE
))
795 userfaultfd_ctx_get(ctx
);
796 WRITE_ONCE(ctx
->mmap_changing
, true);
797 up_read(&mm
->mmap_sem
);
801 ewq
.msg
.event
= UFFD_EVENT_REMOVE
;
802 ewq
.msg
.arg
.remove
.start
= start
;
803 ewq
.msg
.arg
.remove
.end
= end
;
805 userfaultfd_event_wait_completion(ctx
, &ewq
);
810 static bool has_unmap_ctx(struct userfaultfd_ctx
*ctx
, struct list_head
*unmaps
,
811 unsigned long start
, unsigned long end
)
813 struct userfaultfd_unmap_ctx
*unmap_ctx
;
815 list_for_each_entry(unmap_ctx
, unmaps
, list
)
816 if (unmap_ctx
->ctx
== ctx
&& unmap_ctx
->start
== start
&&
817 unmap_ctx
->end
== end
)
823 int userfaultfd_unmap_prep(struct vm_area_struct
*vma
,
824 unsigned long start
, unsigned long end
,
825 struct list_head
*unmaps
)
827 for ( ; vma
&& vma
->vm_start
< end
; vma
= vma
->vm_next
) {
828 struct userfaultfd_unmap_ctx
*unmap_ctx
;
829 struct userfaultfd_ctx
*ctx
= vma
->vm_userfaultfd_ctx
.ctx
;
831 if (!ctx
|| !(ctx
->features
& UFFD_FEATURE_EVENT_UNMAP
) ||
832 has_unmap_ctx(ctx
, unmaps
, start
, end
))
835 unmap_ctx
= kzalloc(sizeof(*unmap_ctx
), GFP_KERNEL
);
839 userfaultfd_ctx_get(ctx
);
840 WRITE_ONCE(ctx
->mmap_changing
, true);
841 unmap_ctx
->ctx
= ctx
;
842 unmap_ctx
->start
= start
;
843 unmap_ctx
->end
= end
;
844 list_add_tail(&unmap_ctx
->list
, unmaps
);
850 void userfaultfd_unmap_complete(struct mm_struct
*mm
, struct list_head
*uf
)
852 struct userfaultfd_unmap_ctx
*ctx
, *n
;
853 struct userfaultfd_wait_queue ewq
;
855 list_for_each_entry_safe(ctx
, n
, uf
, list
) {
858 ewq
.msg
.event
= UFFD_EVENT_UNMAP
;
859 ewq
.msg
.arg
.remove
.start
= ctx
->start
;
860 ewq
.msg
.arg
.remove
.end
= ctx
->end
;
862 userfaultfd_event_wait_completion(ctx
->ctx
, &ewq
);
864 list_del(&ctx
->list
);
869 static int userfaultfd_release(struct inode
*inode
, struct file
*file
)
871 struct userfaultfd_ctx
*ctx
= file
->private_data
;
872 struct mm_struct
*mm
= ctx
->mm
;
873 struct vm_area_struct
*vma
, *prev
;
874 /* len == 0 means wake all */
875 struct userfaultfd_wake_range range
= { .len
= 0, };
876 unsigned long new_flags
;
879 WRITE_ONCE(ctx
->released
, true);
881 if (!mmget_not_zero(mm
))
885 * Flush page faults out of all CPUs. NOTE: all page faults
886 * must be retried without returning VM_FAULT_SIGBUS if
887 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
888 * changes while handle_userfault released the mmap_sem. So
889 * it's critical that released is set to true (above), before
890 * taking the mmap_sem for writing.
892 down_write(&mm
->mmap_sem
);
893 still_valid
= mmget_still_valid(mm
);
895 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
) {
897 BUG_ON(!!vma
->vm_userfaultfd_ctx
.ctx
^
898 !!(vma
->vm_flags
& (VM_UFFD_MISSING
| VM_UFFD_WP
)));
899 if (vma
->vm_userfaultfd_ctx
.ctx
!= ctx
) {
903 new_flags
= vma
->vm_flags
& ~(VM_UFFD_MISSING
| VM_UFFD_WP
);
905 prev
= vma_merge(mm
, prev
, vma
->vm_start
, vma
->vm_end
,
906 new_flags
, vma
->anon_vma
,
907 vma
->vm_file
, vma
->vm_pgoff
,
915 vma
->vm_flags
= new_flags
;
916 vma
->vm_userfaultfd_ctx
= NULL_VM_UFFD_CTX
;
918 up_write(&mm
->mmap_sem
);
922 * After no new page faults can wait on this fault_*wqh, flush
923 * the last page faults that may have been already waiting on
926 spin_lock_irq(&ctx
->fault_pending_wqh
.lock
);
927 __wake_up_locked_key(&ctx
->fault_pending_wqh
, TASK_NORMAL
, &range
);
928 __wake_up(&ctx
->fault_wqh
, TASK_NORMAL
, 1, &range
);
929 spin_unlock_irq(&ctx
->fault_pending_wqh
.lock
);
931 /* Flush pending events that may still wait on event_wqh */
932 wake_up_all(&ctx
->event_wqh
);
934 wake_up_poll(&ctx
->fd_wqh
, EPOLLHUP
);
935 userfaultfd_ctx_put(ctx
);
939 /* fault_pending_wqh.lock must be hold by the caller */
940 static inline struct userfaultfd_wait_queue
*find_userfault_in(
941 wait_queue_head_t
*wqh
)
943 wait_queue_entry_t
*wq
;
944 struct userfaultfd_wait_queue
*uwq
;
946 lockdep_assert_held(&wqh
->lock
);
949 if (!waitqueue_active(wqh
))
951 /* walk in reverse to provide FIFO behavior to read userfaults */
952 wq
= list_last_entry(&wqh
->head
, typeof(*wq
), entry
);
953 uwq
= container_of(wq
, struct userfaultfd_wait_queue
, wq
);
958 static inline struct userfaultfd_wait_queue
*find_userfault(
959 struct userfaultfd_ctx
*ctx
)
961 return find_userfault_in(&ctx
->fault_pending_wqh
);
964 static inline struct userfaultfd_wait_queue
*find_userfault_evt(
965 struct userfaultfd_ctx
*ctx
)
967 return find_userfault_in(&ctx
->event_wqh
);
970 static __poll_t
userfaultfd_poll(struct file
*file
, poll_table
*wait
)
972 struct userfaultfd_ctx
*ctx
= file
->private_data
;
975 poll_wait(file
, &ctx
->fd_wqh
, wait
);
977 switch (ctx
->state
) {
978 case UFFD_STATE_WAIT_API
:
980 case UFFD_STATE_RUNNING
:
982 * poll() never guarantees that read won't block.
983 * userfaults can be waken before they're read().
985 if (unlikely(!(file
->f_flags
& O_NONBLOCK
)))
988 * lockless access to see if there are pending faults
989 * __pollwait last action is the add_wait_queue but
990 * the spin_unlock would allow the waitqueue_active to
991 * pass above the actual list_add inside
992 * add_wait_queue critical section. So use a full
993 * memory barrier to serialize the list_add write of
994 * add_wait_queue() with the waitqueue_active read
999 if (waitqueue_active(&ctx
->fault_pending_wqh
))
1001 else if (waitqueue_active(&ctx
->event_wqh
))
1011 static const struct file_operations userfaultfd_fops
;
1013 static int resolve_userfault_fork(struct userfaultfd_ctx
*ctx
,
1014 struct userfaultfd_ctx
*new,
1015 struct uffd_msg
*msg
)
1019 fd
= anon_inode_getfd("[userfaultfd]", &userfaultfd_fops
, new,
1020 O_RDWR
| (new->flags
& UFFD_SHARED_FCNTL_FLAGS
));
1024 msg
->arg
.reserved
.reserved1
= 0;
1025 msg
->arg
.fork
.ufd
= fd
;
1029 static ssize_t
userfaultfd_ctx_read(struct userfaultfd_ctx
*ctx
, int no_wait
,
1030 struct uffd_msg
*msg
)
1033 DECLARE_WAITQUEUE(wait
, current
);
1034 struct userfaultfd_wait_queue
*uwq
;
1036 * Handling fork event requires sleeping operations, so
1037 * we drop the event_wqh lock, then do these ops, then
1038 * lock it back and wake up the waiter. While the lock is
1039 * dropped the ewq may go away so we keep track of it
1042 LIST_HEAD(fork_event
);
1043 struct userfaultfd_ctx
*fork_nctx
= NULL
;
1045 /* always take the fd_wqh lock before the fault_pending_wqh lock */
1046 spin_lock_irq(&ctx
->fd_wqh
.lock
);
1047 __add_wait_queue(&ctx
->fd_wqh
, &wait
);
1049 set_current_state(TASK_INTERRUPTIBLE
);
1050 spin_lock(&ctx
->fault_pending_wqh
.lock
);
1051 uwq
= find_userfault(ctx
);
1054 * Use a seqcount to repeat the lockless check
1055 * in wake_userfault() to avoid missing
1056 * wakeups because during the refile both
1057 * waitqueue could become empty if this is the
1060 write_seqcount_begin(&ctx
->refile_seq
);
1063 * The fault_pending_wqh.lock prevents the uwq
1064 * to disappear from under us.
1066 * Refile this userfault from
1067 * fault_pending_wqh to fault_wqh, it's not
1068 * pending anymore after we read it.
1070 * Use list_del() by hand (as
1071 * userfaultfd_wake_function also uses
1072 * list_del_init() by hand) to be sure nobody
1073 * changes __remove_wait_queue() to use
1074 * list_del_init() in turn breaking the
1075 * !list_empty_careful() check in
1076 * handle_userfault(). The uwq->wq.head list
1077 * must never be empty at any time during the
1078 * refile, or the waitqueue could disappear
1079 * from under us. The "wait_queue_head_t"
1080 * parameter of __remove_wait_queue() is unused
1083 list_del(&uwq
->wq
.entry
);
1084 add_wait_queue(&ctx
->fault_wqh
, &uwq
->wq
);
1086 write_seqcount_end(&ctx
->refile_seq
);
1088 /* careful to always initialize msg if ret == 0 */
1090 spin_unlock(&ctx
->fault_pending_wqh
.lock
);
1094 spin_unlock(&ctx
->fault_pending_wqh
.lock
);
1096 spin_lock(&ctx
->event_wqh
.lock
);
1097 uwq
= find_userfault_evt(ctx
);
1101 if (uwq
->msg
.event
== UFFD_EVENT_FORK
) {
1102 fork_nctx
= (struct userfaultfd_ctx
*)
1104 uwq
->msg
.arg
.reserved
.reserved1
;
1105 list_move(&uwq
->wq
.entry
, &fork_event
);
1107 * fork_nctx can be freed as soon as
1108 * we drop the lock, unless we take a
1111 userfaultfd_ctx_get(fork_nctx
);
1112 spin_unlock(&ctx
->event_wqh
.lock
);
1117 userfaultfd_event_complete(ctx
, uwq
);
1118 spin_unlock(&ctx
->event_wqh
.lock
);
1122 spin_unlock(&ctx
->event_wqh
.lock
);
1124 if (signal_pending(current
)) {
1132 spin_unlock_irq(&ctx
->fd_wqh
.lock
);
1134 spin_lock_irq(&ctx
->fd_wqh
.lock
);
1136 __remove_wait_queue(&ctx
->fd_wqh
, &wait
);
1137 __set_current_state(TASK_RUNNING
);
1138 spin_unlock_irq(&ctx
->fd_wqh
.lock
);
1140 if (!ret
&& msg
->event
== UFFD_EVENT_FORK
) {
1141 ret
= resolve_userfault_fork(ctx
, fork_nctx
, msg
);
1142 spin_lock_irq(&ctx
->event_wqh
.lock
);
1143 if (!list_empty(&fork_event
)) {
1145 * The fork thread didn't abort, so we can
1146 * drop the temporary refcount.
1148 userfaultfd_ctx_put(fork_nctx
);
1150 uwq
= list_first_entry(&fork_event
,
1154 * If fork_event list wasn't empty and in turn
1155 * the event wasn't already released by fork
1156 * (the event is allocated on fork kernel
1157 * stack), put the event back to its place in
1158 * the event_wq. fork_event head will be freed
1159 * as soon as we return so the event cannot
1160 * stay queued there no matter the current
1163 list_del(&uwq
->wq
.entry
);
1164 __add_wait_queue(&ctx
->event_wqh
, &uwq
->wq
);
1167 * Leave the event in the waitqueue and report
1168 * error to userland if we failed to resolve
1169 * the userfault fork.
1172 userfaultfd_event_complete(ctx
, uwq
);
1175 * Here the fork thread aborted and the
1176 * refcount from the fork thread on fork_nctx
1177 * has already been released. We still hold
1178 * the reference we took before releasing the
1179 * lock above. If resolve_userfault_fork
1180 * failed we've to drop it because the
1181 * fork_nctx has to be freed in such case. If
1182 * it succeeded we'll hold it because the new
1183 * uffd references it.
1186 userfaultfd_ctx_put(fork_nctx
);
1188 spin_unlock_irq(&ctx
->event_wqh
.lock
);
1194 static ssize_t
userfaultfd_read(struct file
*file
, char __user
*buf
,
1195 size_t count
, loff_t
*ppos
)
1197 struct userfaultfd_ctx
*ctx
= file
->private_data
;
1198 ssize_t _ret
, ret
= 0;
1199 struct uffd_msg msg
;
1200 int no_wait
= file
->f_flags
& O_NONBLOCK
;
1202 if (ctx
->state
== UFFD_STATE_WAIT_API
)
1206 if (count
< sizeof(msg
))
1207 return ret
? ret
: -EINVAL
;
1208 _ret
= userfaultfd_ctx_read(ctx
, no_wait
, &msg
);
1210 return ret
? ret
: _ret
;
1211 if (copy_to_user((__u64 __user
*) buf
, &msg
, sizeof(msg
)))
1212 return ret
? ret
: -EFAULT
;
1215 count
-= sizeof(msg
);
1217 * Allow to read more than one fault at time but only
1218 * block if waiting for the very first one.
1220 no_wait
= O_NONBLOCK
;
1224 static void __wake_userfault(struct userfaultfd_ctx
*ctx
,
1225 struct userfaultfd_wake_range
*range
)
1227 spin_lock_irq(&ctx
->fault_pending_wqh
.lock
);
1228 /* wake all in the range and autoremove */
1229 if (waitqueue_active(&ctx
->fault_pending_wqh
))
1230 __wake_up_locked_key(&ctx
->fault_pending_wqh
, TASK_NORMAL
,
1232 if (waitqueue_active(&ctx
->fault_wqh
))
1233 __wake_up(&ctx
->fault_wqh
, TASK_NORMAL
, 1, range
);
1234 spin_unlock_irq(&ctx
->fault_pending_wqh
.lock
);
1237 static __always_inline
void wake_userfault(struct userfaultfd_ctx
*ctx
,
1238 struct userfaultfd_wake_range
*range
)
1244 * To be sure waitqueue_active() is not reordered by the CPU
1245 * before the pagetable update, use an explicit SMP memory
1246 * barrier here. PT lock release or up_read(mmap_sem) still
1247 * have release semantics that can allow the
1248 * waitqueue_active() to be reordered before the pte update.
1253 * Use waitqueue_active because it's very frequent to
1254 * change the address space atomically even if there are no
1255 * userfaults yet. So we take the spinlock only when we're
1256 * sure we've userfaults to wake.
1259 seq
= read_seqcount_begin(&ctx
->refile_seq
);
1260 need_wakeup
= waitqueue_active(&ctx
->fault_pending_wqh
) ||
1261 waitqueue_active(&ctx
->fault_wqh
);
1263 } while (read_seqcount_retry(&ctx
->refile_seq
, seq
));
1265 __wake_userfault(ctx
, range
);
1268 static __always_inline
int validate_range(struct mm_struct
*mm
,
1269 __u64
*start
, __u64 len
)
1271 __u64 task_size
= mm
->task_size
;
1273 *start
= untagged_addr(*start
);
1275 if (*start
& ~PAGE_MASK
)
1277 if (len
& ~PAGE_MASK
)
1281 if (*start
< mmap_min_addr
)
1283 if (*start
>= task_size
)
1285 if (len
> task_size
- *start
)
1290 static inline bool vma_can_userfault(struct vm_area_struct
*vma
)
1292 return vma_is_anonymous(vma
) || is_vm_hugetlb_page(vma
) ||
1296 static int userfaultfd_register(struct userfaultfd_ctx
*ctx
,
1299 struct mm_struct
*mm
= ctx
->mm
;
1300 struct vm_area_struct
*vma
, *prev
, *cur
;
1302 struct uffdio_register uffdio_register
;
1303 struct uffdio_register __user
*user_uffdio_register
;
1304 unsigned long vm_flags
, new_flags
;
1307 unsigned long start
, end
, vma_end
;
1309 user_uffdio_register
= (struct uffdio_register __user
*) arg
;
1312 if (copy_from_user(&uffdio_register
, user_uffdio_register
,
1313 sizeof(uffdio_register
)-sizeof(__u64
)))
1317 if (!uffdio_register
.mode
)
1319 if (uffdio_register
.mode
& ~(UFFDIO_REGISTER_MODE_MISSING
|
1320 UFFDIO_REGISTER_MODE_WP
))
1323 if (uffdio_register
.mode
& UFFDIO_REGISTER_MODE_MISSING
)
1324 vm_flags
|= VM_UFFD_MISSING
;
1325 if (uffdio_register
.mode
& UFFDIO_REGISTER_MODE_WP
) {
1326 vm_flags
|= VM_UFFD_WP
;
1328 * FIXME: remove the below error constraint by
1329 * implementing the wprotect tracking mode.
1335 ret
= validate_range(mm
, &uffdio_register
.range
.start
,
1336 uffdio_register
.range
.len
);
1340 start
= uffdio_register
.range
.start
;
1341 end
= start
+ uffdio_register
.range
.len
;
1344 if (!mmget_not_zero(mm
))
1347 down_write(&mm
->mmap_sem
);
1348 if (!mmget_still_valid(mm
))
1350 vma
= find_vma_prev(mm
, start
, &prev
);
1354 /* check that there's at least one vma in the range */
1356 if (vma
->vm_start
>= end
)
1360 * If the first vma contains huge pages, make sure start address
1361 * is aligned to huge page size.
1363 if (is_vm_hugetlb_page(vma
)) {
1364 unsigned long vma_hpagesize
= vma_kernel_pagesize(vma
);
1366 if (start
& (vma_hpagesize
- 1))
1371 * Search for not compatible vmas.
1374 basic_ioctls
= false;
1375 for (cur
= vma
; cur
&& cur
->vm_start
< end
; cur
= cur
->vm_next
) {
1378 BUG_ON(!!cur
->vm_userfaultfd_ctx
.ctx
^
1379 !!(cur
->vm_flags
& (VM_UFFD_MISSING
| VM_UFFD_WP
)));
1381 /* check not compatible vmas */
1383 if (!vma_can_userfault(cur
))
1387 * UFFDIO_COPY will fill file holes even without
1388 * PROT_WRITE. This check enforces that if this is a
1389 * MAP_SHARED, the process has write permission to the backing
1390 * file. If VM_MAYWRITE is set it also enforces that on a
1391 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1392 * F_WRITE_SEAL can be taken until the vma is destroyed.
1395 if (unlikely(!(cur
->vm_flags
& VM_MAYWRITE
)))
1399 * If this vma contains ending address, and huge pages
1402 if (is_vm_hugetlb_page(cur
) && end
<= cur
->vm_end
&&
1403 end
> cur
->vm_start
) {
1404 unsigned long vma_hpagesize
= vma_kernel_pagesize(cur
);
1408 if (end
& (vma_hpagesize
- 1))
1413 * Check that this vma isn't already owned by a
1414 * different userfaultfd. We can't allow more than one
1415 * userfaultfd to own a single vma simultaneously or we
1416 * wouldn't know which one to deliver the userfaults to.
1419 if (cur
->vm_userfaultfd_ctx
.ctx
&&
1420 cur
->vm_userfaultfd_ctx
.ctx
!= ctx
)
1424 * Note vmas containing huge pages
1426 if (is_vm_hugetlb_page(cur
))
1427 basic_ioctls
= true;
1433 if (vma
->vm_start
< start
)
1440 BUG_ON(!vma_can_userfault(vma
));
1441 BUG_ON(vma
->vm_userfaultfd_ctx
.ctx
&&
1442 vma
->vm_userfaultfd_ctx
.ctx
!= ctx
);
1443 WARN_ON(!(vma
->vm_flags
& VM_MAYWRITE
));
1446 * Nothing to do: this vma is already registered into this
1447 * userfaultfd and with the right tracking mode too.
1449 if (vma
->vm_userfaultfd_ctx
.ctx
== ctx
&&
1450 (vma
->vm_flags
& vm_flags
) == vm_flags
)
1453 if (vma
->vm_start
> start
)
1454 start
= vma
->vm_start
;
1455 vma_end
= min(end
, vma
->vm_end
);
1457 new_flags
= (vma
->vm_flags
&
1458 ~(VM_UFFD_MISSING
|VM_UFFD_WP
)) | vm_flags
;
1459 prev
= vma_merge(mm
, prev
, start
, vma_end
, new_flags
,
1460 vma
->anon_vma
, vma
->vm_file
, vma
->vm_pgoff
,
1462 ((struct vm_userfaultfd_ctx
){ ctx
}));
1467 if (vma
->vm_start
< start
) {
1468 ret
= split_vma(mm
, vma
, start
, 1);
1472 if (vma
->vm_end
> end
) {
1473 ret
= split_vma(mm
, vma
, end
, 0);
1479 * In the vma_merge() successful mprotect-like case 8:
1480 * the next vma was merged into the current one and
1481 * the current one has not been updated yet.
1483 vma
->vm_flags
= new_flags
;
1484 vma
->vm_userfaultfd_ctx
.ctx
= ctx
;
1488 start
= vma
->vm_end
;
1490 } while (vma
&& vma
->vm_start
< end
);
1492 up_write(&mm
->mmap_sem
);
1496 * Now that we scanned all vmas we can already tell
1497 * userland which ioctls methods are guaranteed to
1498 * succeed on this range.
1500 if (put_user(basic_ioctls
? UFFD_API_RANGE_IOCTLS_BASIC
:
1501 UFFD_API_RANGE_IOCTLS
,
1502 &user_uffdio_register
->ioctls
))
1509 static int userfaultfd_unregister(struct userfaultfd_ctx
*ctx
,
1512 struct mm_struct
*mm
= ctx
->mm
;
1513 struct vm_area_struct
*vma
, *prev
, *cur
;
1515 struct uffdio_range uffdio_unregister
;
1516 unsigned long new_flags
;
1518 unsigned long start
, end
, vma_end
;
1519 const void __user
*buf
= (void __user
*)arg
;
1522 if (copy_from_user(&uffdio_unregister
, buf
, sizeof(uffdio_unregister
)))
1525 ret
= validate_range(mm
, &uffdio_unregister
.start
,
1526 uffdio_unregister
.len
);
1530 start
= uffdio_unregister
.start
;
1531 end
= start
+ uffdio_unregister
.len
;
1534 if (!mmget_not_zero(mm
))
1537 down_write(&mm
->mmap_sem
);
1538 if (!mmget_still_valid(mm
))
1540 vma
= find_vma_prev(mm
, start
, &prev
);
1544 /* check that there's at least one vma in the range */
1546 if (vma
->vm_start
>= end
)
1550 * If the first vma contains huge pages, make sure start address
1551 * is aligned to huge page size.
1553 if (is_vm_hugetlb_page(vma
)) {
1554 unsigned long vma_hpagesize
= vma_kernel_pagesize(vma
);
1556 if (start
& (vma_hpagesize
- 1))
1561 * Search for not compatible vmas.
1565 for (cur
= vma
; cur
&& cur
->vm_start
< end
; cur
= cur
->vm_next
) {
1568 BUG_ON(!!cur
->vm_userfaultfd_ctx
.ctx
^
1569 !!(cur
->vm_flags
& (VM_UFFD_MISSING
| VM_UFFD_WP
)));
1572 * Check not compatible vmas, not strictly required
1573 * here as not compatible vmas cannot have an
1574 * userfaultfd_ctx registered on them, but this
1575 * provides for more strict behavior to notice
1576 * unregistration errors.
1578 if (!vma_can_userfault(cur
))
1585 if (vma
->vm_start
< start
)
1592 BUG_ON(!vma_can_userfault(vma
));
1595 * Nothing to do: this vma is already registered into this
1596 * userfaultfd and with the right tracking mode too.
1598 if (!vma
->vm_userfaultfd_ctx
.ctx
)
1601 WARN_ON(!(vma
->vm_flags
& VM_MAYWRITE
));
1603 if (vma
->vm_start
> start
)
1604 start
= vma
->vm_start
;
1605 vma_end
= min(end
, vma
->vm_end
);
1607 if (userfaultfd_missing(vma
)) {
1609 * Wake any concurrent pending userfault while
1610 * we unregister, so they will not hang
1611 * permanently and it avoids userland to call
1612 * UFFDIO_WAKE explicitly.
1614 struct userfaultfd_wake_range range
;
1615 range
.start
= start
;
1616 range
.len
= vma_end
- start
;
1617 wake_userfault(vma
->vm_userfaultfd_ctx
.ctx
, &range
);
1620 new_flags
= vma
->vm_flags
& ~(VM_UFFD_MISSING
| VM_UFFD_WP
);
1621 prev
= vma_merge(mm
, prev
, start
, vma_end
, new_flags
,
1622 vma
->anon_vma
, vma
->vm_file
, vma
->vm_pgoff
,
1629 if (vma
->vm_start
< start
) {
1630 ret
= split_vma(mm
, vma
, start
, 1);
1634 if (vma
->vm_end
> end
) {
1635 ret
= split_vma(mm
, vma
, end
, 0);
1641 * In the vma_merge() successful mprotect-like case 8:
1642 * the next vma was merged into the current one and
1643 * the current one has not been updated yet.
1645 vma
->vm_flags
= new_flags
;
1646 vma
->vm_userfaultfd_ctx
= NULL_VM_UFFD_CTX
;
1650 start
= vma
->vm_end
;
1652 } while (vma
&& vma
->vm_start
< end
);
1654 up_write(&mm
->mmap_sem
);
1661 * userfaultfd_wake may be used in combination with the
1662 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1664 static int userfaultfd_wake(struct userfaultfd_ctx
*ctx
,
1668 struct uffdio_range uffdio_wake
;
1669 struct userfaultfd_wake_range range
;
1670 const void __user
*buf
= (void __user
*)arg
;
1673 if (copy_from_user(&uffdio_wake
, buf
, sizeof(uffdio_wake
)))
1676 ret
= validate_range(ctx
->mm
, &uffdio_wake
.start
, uffdio_wake
.len
);
1680 range
.start
= uffdio_wake
.start
;
1681 range
.len
= uffdio_wake
.len
;
1684 * len == 0 means wake all and we don't want to wake all here,
1685 * so check it again to be sure.
1687 VM_BUG_ON(!range
.len
);
1689 wake_userfault(ctx
, &range
);
1696 static int userfaultfd_copy(struct userfaultfd_ctx
*ctx
,
1700 struct uffdio_copy uffdio_copy
;
1701 struct uffdio_copy __user
*user_uffdio_copy
;
1702 struct userfaultfd_wake_range range
;
1704 user_uffdio_copy
= (struct uffdio_copy __user
*) arg
;
1707 if (READ_ONCE(ctx
->mmap_changing
))
1711 if (copy_from_user(&uffdio_copy
, user_uffdio_copy
,
1712 /* don't copy "copy" last field */
1713 sizeof(uffdio_copy
)-sizeof(__s64
)))
1716 ret
= validate_range(ctx
->mm
, &uffdio_copy
.dst
, uffdio_copy
.len
);
1720 * double check for wraparound just in case. copy_from_user()
1721 * will later check uffdio_copy.src + uffdio_copy.len to fit
1722 * in the userland range.
1725 if (uffdio_copy
.src
+ uffdio_copy
.len
<= uffdio_copy
.src
)
1727 if (uffdio_copy
.mode
& ~UFFDIO_COPY_MODE_DONTWAKE
)
1729 if (mmget_not_zero(ctx
->mm
)) {
1730 ret
= mcopy_atomic(ctx
->mm
, uffdio_copy
.dst
, uffdio_copy
.src
,
1731 uffdio_copy
.len
, &ctx
->mmap_changing
);
1736 if (unlikely(put_user(ret
, &user_uffdio_copy
->copy
)))
1741 /* len == 0 would wake all */
1743 if (!(uffdio_copy
.mode
& UFFDIO_COPY_MODE_DONTWAKE
)) {
1744 range
.start
= uffdio_copy
.dst
;
1745 wake_userfault(ctx
, &range
);
1747 ret
= range
.len
== uffdio_copy
.len
? 0 : -EAGAIN
;
1752 static int userfaultfd_zeropage(struct userfaultfd_ctx
*ctx
,
1756 struct uffdio_zeropage uffdio_zeropage
;
1757 struct uffdio_zeropage __user
*user_uffdio_zeropage
;
1758 struct userfaultfd_wake_range range
;
1760 user_uffdio_zeropage
= (struct uffdio_zeropage __user
*) arg
;
1763 if (READ_ONCE(ctx
->mmap_changing
))
1767 if (copy_from_user(&uffdio_zeropage
, user_uffdio_zeropage
,
1768 /* don't copy "zeropage" last field */
1769 sizeof(uffdio_zeropage
)-sizeof(__s64
)))
1772 ret
= validate_range(ctx
->mm
, &uffdio_zeropage
.range
.start
,
1773 uffdio_zeropage
.range
.len
);
1777 if (uffdio_zeropage
.mode
& ~UFFDIO_ZEROPAGE_MODE_DONTWAKE
)
1780 if (mmget_not_zero(ctx
->mm
)) {
1781 ret
= mfill_zeropage(ctx
->mm
, uffdio_zeropage
.range
.start
,
1782 uffdio_zeropage
.range
.len
,
1783 &ctx
->mmap_changing
);
1788 if (unlikely(put_user(ret
, &user_uffdio_zeropage
->zeropage
)))
1792 /* len == 0 would wake all */
1795 if (!(uffdio_zeropage
.mode
& UFFDIO_ZEROPAGE_MODE_DONTWAKE
)) {
1796 range
.start
= uffdio_zeropage
.range
.start
;
1797 wake_userfault(ctx
, &range
);
1799 ret
= range
.len
== uffdio_zeropage
.range
.len
? 0 : -EAGAIN
;
1804 static inline unsigned int uffd_ctx_features(__u64 user_features
)
1807 * For the current set of features the bits just coincide
1809 return (unsigned int)user_features
;
1813 * userland asks for a certain API version and we return which bits
1814 * and ioctl commands are implemented in this kernel for such API
1815 * version or -EINVAL if unknown.
1817 static int userfaultfd_api(struct userfaultfd_ctx
*ctx
,
1820 struct uffdio_api uffdio_api
;
1821 void __user
*buf
= (void __user
*)arg
;
1826 if (ctx
->state
!= UFFD_STATE_WAIT_API
)
1829 if (copy_from_user(&uffdio_api
, buf
, sizeof(uffdio_api
)))
1831 features
= uffdio_api
.features
;
1833 if (uffdio_api
.api
!= UFFD_API
|| (features
& ~UFFD_API_FEATURES
))
1836 if ((features
& UFFD_FEATURE_EVENT_FORK
) && !capable(CAP_SYS_PTRACE
))
1838 /* report all available features and ioctls to userland */
1839 uffdio_api
.features
= UFFD_API_FEATURES
;
1840 uffdio_api
.ioctls
= UFFD_API_IOCTLS
;
1842 if (copy_to_user(buf
, &uffdio_api
, sizeof(uffdio_api
)))
1844 ctx
->state
= UFFD_STATE_RUNNING
;
1845 /* only enable the requested features for this uffd context */
1846 ctx
->features
= uffd_ctx_features(features
);
1851 memset(&uffdio_api
, 0, sizeof(uffdio_api
));
1852 if (copy_to_user(buf
, &uffdio_api
, sizeof(uffdio_api
)))
1857 static long userfaultfd_ioctl(struct file
*file
, unsigned cmd
,
1861 struct userfaultfd_ctx
*ctx
= file
->private_data
;
1863 if (cmd
!= UFFDIO_API
&& ctx
->state
== UFFD_STATE_WAIT_API
)
1868 ret
= userfaultfd_api(ctx
, arg
);
1870 case UFFDIO_REGISTER
:
1871 ret
= userfaultfd_register(ctx
, arg
);
1873 case UFFDIO_UNREGISTER
:
1874 ret
= userfaultfd_unregister(ctx
, arg
);
1877 ret
= userfaultfd_wake(ctx
, arg
);
1880 ret
= userfaultfd_copy(ctx
, arg
);
1882 case UFFDIO_ZEROPAGE
:
1883 ret
= userfaultfd_zeropage(ctx
, arg
);
1889 #ifdef CONFIG_PROC_FS
1890 static void userfaultfd_show_fdinfo(struct seq_file
*m
, struct file
*f
)
1892 struct userfaultfd_ctx
*ctx
= f
->private_data
;
1893 wait_queue_entry_t
*wq
;
1894 unsigned long pending
= 0, total
= 0;
1896 spin_lock_irq(&ctx
->fault_pending_wqh
.lock
);
1897 list_for_each_entry(wq
, &ctx
->fault_pending_wqh
.head
, entry
) {
1901 list_for_each_entry(wq
, &ctx
->fault_wqh
.head
, entry
) {
1904 spin_unlock_irq(&ctx
->fault_pending_wqh
.lock
);
1907 * If more protocols will be added, there will be all shown
1908 * separated by a space. Like this:
1909 * protocols: aa:... bb:...
1911 seq_printf(m
, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1912 pending
, total
, UFFD_API
, ctx
->features
,
1913 UFFD_API_IOCTLS
|UFFD_API_RANGE_IOCTLS
);
1917 static const struct file_operations userfaultfd_fops
= {
1918 #ifdef CONFIG_PROC_FS
1919 .show_fdinfo
= userfaultfd_show_fdinfo
,
1921 .release
= userfaultfd_release
,
1922 .poll
= userfaultfd_poll
,
1923 .read
= userfaultfd_read
,
1924 .unlocked_ioctl
= userfaultfd_ioctl
,
1925 .compat_ioctl
= compat_ptr_ioctl
,
1926 .llseek
= noop_llseek
,
1929 static void init_once_userfaultfd_ctx(void *mem
)
1931 struct userfaultfd_ctx
*ctx
= (struct userfaultfd_ctx
*) mem
;
1933 init_waitqueue_head(&ctx
->fault_pending_wqh
);
1934 init_waitqueue_head(&ctx
->fault_wqh
);
1935 init_waitqueue_head(&ctx
->event_wqh
);
1936 init_waitqueue_head(&ctx
->fd_wqh
);
1937 seqcount_init(&ctx
->refile_seq
);
1940 SYSCALL_DEFINE1(userfaultfd
, int, flags
)
1942 struct userfaultfd_ctx
*ctx
;
1945 if (!sysctl_unprivileged_userfaultfd
&& !capable(CAP_SYS_PTRACE
))
1948 BUG_ON(!current
->mm
);
1950 /* Check the UFFD_* constants for consistency. */
1951 BUILD_BUG_ON(UFFD_CLOEXEC
!= O_CLOEXEC
);
1952 BUILD_BUG_ON(UFFD_NONBLOCK
!= O_NONBLOCK
);
1954 if (flags
& ~UFFD_SHARED_FCNTL_FLAGS
)
1957 ctx
= kmem_cache_alloc(userfaultfd_ctx_cachep
, GFP_KERNEL
);
1961 refcount_set(&ctx
->refcount
, 1);
1964 ctx
->state
= UFFD_STATE_WAIT_API
;
1965 ctx
->released
= false;
1966 ctx
->mmap_changing
= false;
1967 ctx
->mm
= current
->mm
;
1968 /* prevent the mm struct to be freed */
1971 fd
= anon_inode_getfd("[userfaultfd]", &userfaultfd_fops
, ctx
,
1972 O_RDWR
| (flags
& UFFD_SHARED_FCNTL_FLAGS
));
1975 kmem_cache_free(userfaultfd_ctx_cachep
, ctx
);
1980 static int __init
userfaultfd_init(void)
1982 userfaultfd_ctx_cachep
= kmem_cache_create("userfaultfd_ctx_cache",
1983 sizeof(struct userfaultfd_ctx
),
1985 SLAB_HWCACHE_ALIGN
|SLAB_PANIC
,
1986 init_once_userfaultfd_ctx
);
1989 __initcall(userfaultfd_init
);